Paint colors are usually displayed and marketed to consumers using color sampling display products such as color cards, color chips or color swatches, via paint samples applied to or deposited on various substrates, including paper cards. Due to environmental restrictions, there is a significant need for lower volatile organic compound-containing (VOC-containing) paints, including in color display devices. Typically, lower VOC-containing coatings do not provide the physical characteristics or mechanical performance needed for color sampling display devices or color cards.
In an effort to provide a low VOC- or zero VOC-containing system with high performance, manufacturers have been using water-based polyurethanes. These water-based polyurethanes are usually linear polymers and produce films that have chemical resistance lower than the highly crosslinked films of solvent-based urethane systems. Preparing the polyurethane coating compositions by pre-crosslinking a water-based polyurethane polymer may be accomplished by incorporating a large amount of monomers that have more than two reactive functional groups in the prepolymer stage. However, this results in highly viscous prepolymer blends that cannot be easily dispersed in water. Reactive diluents can be used to address the viscosity problem, but these diluents may be highly irritating to the eyes, skin, or both, and extensive and impractical industrial hygiene measures are required to use these products.
Moreover, when water-based polyurethane polymers are applied to certain substrates, such as paper, for example, along with the dyes or colorants needed to manufacture a color sampling product, the paper will tend to wrinkle, buckle or curl. Sizing or treating paper to reduce absorption of water is time-consuming and does not necessarily prevent the buckling or curling of the paper. The presence of water in the polymers has severe impact on both the mechanical performance of the color display device and on its aesthetic appeal.
Therefore, what is needed are high-performance low VOC- or zero VOC-containing compositions that can be applied and cured to an untreated paper substrate to form a color display product or color sampling product with mechanical integrity and aesthetic appeal.